Removal of tramp material from fluid bed vessels

ABSTRACT

A system for removal of tramp or trash material from a single fluidized bed contained within a single vessel used to incinerate or pyrolyze solid fuel, the system comprises a gently sloped, skewed or serpentine stationary bed support and air distributor structure which distributes air in a fashion so as to uniformly fluidize a shallow bed of variable depth across the slope thereof without internally circulating the bed, and at the same time cause non-combustible tramp or trash material (e.g. pieces of steel, rocks, clumps, etc.), to be removed from the bed without passing to a location either above or beneath the bed. The angle of slope is strictly controlled. During periods of non-fluidization and/or non-use, the bed material is kept from falling into the air distribution plenum below the bed support structure by hollow bed containment structure disposed at sites below the bed support structure. Fluidizing air and gravity alone gently walk tramp material downwardly along the top of the bed support structure toward a discharge site. Although the discharge of fluidized air through the grid plate into the bed may be non-vertical, the horizontal component of said air discharge is immediately dissipated and the bed turbulence or direction of fluidization is essentially vertical. The sizing and spacing of air distributor holes may be varied in respect to any sloped grid plate to provide for proper and uniform fluidization across the bed having non-uniform depth without causing rotational mixing within the bed.

BACKGROUND Continuity

This application is a division of U.S. patent application Ser. No.619,678, filed June 11, 1984, now U.S. Pat. No. 4,553,487, which is acontinuation-in-part of copending U.S. patent application Ser. No.528,815, filed Sept. 2, 1983, now abandoned.

FIELD OF INVENTION

The present invention relates broadly to fluidized bed combustion andpyrolysis and more particularly to a novel system, including method andapparatus, for effectively removing tramp or trash material from the bedmaterial while avoiding certain problems encountered by the prior art.

PRIOR ART

As can be appreciated by reference to U.S. Pat. Nos. 3,834,326;4,060,041 and 4,075,953, fluidized bed systems typically require, interalia, a bed vessel, a fluidizing air distribution structure, bedmaterial of predetermined depth, a preheater and an ongoing source offuel to be incinerated or pyrolized within the bed.

Bed support structure or a grid plate (aka a gas/air distributor) is animportant and necessary part of such fluidized bed systems. There aretwo basic types of bed support structures or grid plates used today.These are illustrated in FIGS. 1 and 2. FIG. 1 illustrates ahorizontally disposed grid plate. See U.S. Pat. No. 3,834,326, FIG. 1 ofU.S. Pat. No. 4,060,041 and FIG. 1 of U.S. Pat. No. 4,075,953. The platehas a dual function. It supports the bed, and it distributes airthroughout the bottom of the bed. When the fluidized bed is used as acombustor, the type of fuel used is ordinarily limited to gases,liquids, or solids, which, when burned, ideally leaves no residue.

Many types of solid materials are used as fuel, but they may and usuallydo, contain tramp or trash material that does not burn. When solid fuelis used in a fluidized bed combustor having a bed support-airdistributor or grid plate, unburned trash or tramp materialprogressively collects on top of the plate. When too much trash hasaccumulated on top of the plate, air distribution through the bedbecomes poor and combustion efficiency drops. With previously proposedsupport plate designs, the accumulated tramp material is difficult andsometimes impossible to remove from above the plate in the bed vessel.

FIG. 2 illustrates an air distribution header system, which distributesair in a fluidized bed. See FIGS. 10 and 11 of U.S. Pat. Nos. 4,060,041and 4,075,953. With it, fluidizing air is distributed into the bedthrough evenly spaced headers, which run from one side of the vessel tothe other. Small air outlet "nozzles" or "distributor caps" are spacedon top of stand pipes projecting upwardly from the headers. Air leavesthe nozzles, or caps, and fluidizes the bed above. No fluidization takesplace below the outlets of the nozzles or distributor caps.

Sufficient space is left between the headers so that non-fluidizabletramp or trash material comingled with influent solid fuel typicallywill settle between the headers and the distributor nozzles. Atappropriate intervals or continuously, bed material and tramp materialare simultaneously discharged from the vessel through a conical sectionlocated underneath the headers.

Certain types of large, heavy and/or irregularly-shaped trash objectscomingled with the fuel tend to remain lodged in the bed and to clog theopenings between the headers. Eventually, this unfluidizable trampmaterial causes poor bed fluidization and it becomes difficult, if notimpossible, to drain the clogged tramp material from the bed withoutshutting down the system. It has been further proposed in the prior art(i.e. U.S. Pat. No. 4,277,222) that a sloped air diffuser plate be usedin a fluidized bed system wherein the flow of fluidizing air is uneven,resulting in circulation of the bed oppositely above and below bedbaffles generally around a horizontal axis between non-fluidized quietzones of the bed and the fluidized region. Additional baffle materialstructure above the bed baffles the bed in as it circulates to therebycontrol the path of circulation and to confine the bed material to apredetermined location.

During periods when the system is not in use or during operation whenthe system malfunctions and fluidization is improper, bed material, dueto the force of gravity will flow into the air plenum below the diffuserplate.

Also, in a context where sulfur in coal is to be removed in a verticallyfluidized bed using limestone or the like, it has been proposed (in U.S.Pat. Nos. 3,625,164 and 4,419,940) that a traveling grate comprising topand bottom tracks be used. Ash, Ca S, incompletely combusted fuel,tramp, agglomerates and bed material are displaced counter to gravityalong the incline of the moving grate to a dump site for a dischargechute. No provision is made to prevent leakage of bed material into theair plenum below the traveling grate.

Furthermore, it has heen proposed in (U.S. Pat. No. 4,196,676) that ahorizontal fluidized bed grid plate be used in conjunction withdiagonally directed diffuser air, the air being displaced at rates sothat fluidization is not uniform and the bed and foreign objects arecirculated, around a horizontal plane, along two elongated horizontalpaths, one above the other. Bed material elutriated above the bed isreturned to the bed by secondary air flow. Bed material progressivelyremoved, with foreign objects, from the circulating horizontal bedsolely by the force of diffuser air through a downwardly directed chuteis said to return to the bed by upward elutriation within the chute. Theforeign objects (and any bed media not returned to the circulatory bed)are quenched in a bath 43. The proposal of U.S. Pat. No. 4,273,073, isvery similar in respect to non-uniform fluidization and bed circulation,among other things.

In addition, U.S. Pat. No. 3,877,397 proposes use of massive amounts ofbed material in a non-fluidized region in conjunction with two fluidizedbeds, having separate grid plates, each disposed at a very steep anglein respect to the horizontal and where the mass of downstream bed mediacontrols the rate of displacement of bed media and foreign objects asopposed to grid plate angle.

Other proposals exist for use of a sloped air diffuser plate inconjunction with a dynamically circulated fluidized bed which isnon-uniformly fluidized. See the publication Advances in EnergyProduction, from the proceedings of the 5th World Energy EngineeringCongress, Sept. 14-17, 1982. Here, as in other proposals, the vessel ismaterially constricted in the vapor space above the fluidized bed so asto form a deflector wall which, in conjunction with secondary air,controls and confines the circulation of the bed.

Serpentine delivery of compacted municipal waste, under force of thecompaction of continually influent waste, through the vapor space anon-fluid bed pyrolyzer where pyrolysis is completed on a steppedgrating has been proposed in U.S. Pat. No. 4,308,807. The proposal isnot comparable to fluid bed operation and where use of bed media alongthe serpentine path would not work.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

In brief summary, the present invention provides for removal of tramp ortrash material from a single fluidized bed contained within a singlevessel used to incinerate or pyrolyze solid fuel without the attendingdisadvantages of prior fluid bed proposals. In its preferred form, thepresent invention comprises a gently sloped or skewed bed support andair distributor structure designed to distribute air in a fashion as touniformly fluidize a shallow bed of variable depth across the slopethereof without circulating the bed, and at the same time causenon-combustible tramp or trash material (e.g. pieces of steel, rocks,clumps, etc.), to be removed from the bed without passing to a locationeither above or beneath the bed. The angle of slope is strictlycontrolled and is substantially less than the angle of repose of the bedmaterial. The solid fuel is evenly distributed within the bed and is notcompacted into a single mass. The bed support and air distributorstructure has no need for bubble caps or stand pipes or nozzles.Therefore, it is not necessary to have projections or interferences uponor against which incombustible material may accumulate or collect.

During periods of non-fluidization and/or non-use, the bed material iskept from falling into the air distribution plenum below the bed supportstructure by hollow bed containment structure disposed at sites belowthe bed support structure. Said structure accumulates a limited amountof bed material which creates a clog, thereby preventing further flow ofbed material. When use or fluidization is resumed, fluidizing airpneumatically displaces the limited amount of accumulated bed materialfrom said structure to the main body of bed material disposed upon thebed support structure.

The bed support structure is stationary and preferably comprises airdistributor holes disposed at right angles to the slope of the bedsupport structure. The entirety of the bed is fluidized in a uniform andnon-circulating manner. Thus, air enters the bed in one or morenon-vertical directions. This non-vertical air displacement iscontrolled to gently aid in walking tramp material downwardly along thetop of the bed support structure toward a discharge site. The dischargesite is juxtaposed fluidization holes in the grid plate and no mass ofbed material downstream of the region of fluidization is required.Although the discharge of fluidized air through the grid plate into thebed may be non-vertical, the horizontal component of said air dischargeis immediately dissipated and the bed turbulence or direction offluidization is essentially vertical. Secondary air is not required fortramp removal.

In one form, the present invention comprises bed path deflecting meansattached to the top of a sloped bed support plate. In another presentlypreferred form, a sloped helical diffusion plate in the lower part ofthe vessel is provided. This insures sufficient bed dwell time for thefuel to properly incinerate or pyrolyze, while also insuring timelyserpentine, removal of tramp material solely by the forces of gravityand fluidization air without turbulent mixing or circulation of the bed,all in such a fashion that proper and uniform bed fluidization ismaintained.

The sizing and spacing of air distributor holes may be established inrespect to any sloped grid plate in accordance with the presentinvention so as to provide for proper and uniform fluidization acrossthe bed having non-uniform depth without causing rotational mixingwithin the bed.

With the foregoing in mind, it is a primary object of the presentinvention to provide a novel fluidized bed system, including method andapparatus, for removal of tramp or trash material from the bed.

It is a further important object of the invention to provide fluidizingbed structure, and related methods, which gravitationally andefficiently removes tramp material without the disadvantages of theprior art.

It is an additional significant object of the present invention toprovide a fluidized bed system which achieves removal of tramp materialwithout requiring that the tramp material pass to a site below or abovethe bed.

A further dominant object of the present invention is the provision of anovel fluidized bed system which comprises a gently sloped bed supportand fluidizing air structure.

An additional important object of the present invention is the provisionof a fluidized bed having a variable though shallow depth in whichuniform fluidization occurs across the entirety thereof.

An additional paramount object of the present invention is the provisionof a novel bed support and air fluidizing structure wherein bed materialdoes not significantly pass to a site below the bed support and airdistributor structure or materially downstream of the fluidized portionof the bed during intervals of non-use and/or non-fluidization.

An additional object is the provision of novel gently sloped bed supportstructure wherein fluidizing air enters the bed in one or morenon-vertical directions aiding in gentle walking of tramp material fromthe bed downwardly along the sloped bed support toward a discharge sitewhile maintaining uniform fluidization solely in an essentially verticaldirection.

A further object of the present invention is the provision of sloped bedsupport structure by which tramp material is removed from the bed solelyby the forces of fluidizing air and gravity.

A further object is the provision of structure by which the dwell timeof solid fuel particles in the bed is controlled to insure properincineration or pyrolysis.

It is a further significant object of this invention to provide a novelsingle vessel fluid bed system having one or more of the followingfeatures:

(a) gently sloped or skewed stationary bed support and air fluidizationstructure which uniformly essentially vertically fluidized the entiretyof a shallow bed of variable depth without causing the bed to internallycirculate;

(b) capacity to remove non-combustible tramp objects from the bedwithout passing bed media or the tramp to a site either above or belowthe bed;

(c) sloped grid plate the angle of which is strictly controlled and issubstantially less than the angle of repose of the bed material;

(d) incinerates and/or pyrolyzes solid fuel as independent particlesevenly distributed in the bed and not as a single compacted mass;

(e) hollow bed containment structure associated with a grid plate whichprevent loss of bed media into the air plenum during periods of non-useand/or non-fluidization;

(f) whereby tramp material is removed solely by the forces of gravityand fluidizing air;

(g) wherein the bed fluidization is essentially vertical at all timesand tramp objects are gently walked down a sloped air diffuser platesolely by the forces of gravity and fluidizing air;

(h) wherein bed deflecting means and/or circuitous diffuser plate meansare used;

(i) wherein the bed is shallow and use of a mass of bed materialdownstream of the fluidized site is avoided.

(j) wherein the sizing and spacing of air distributor holes is nonuniform to achieve uniform fluidization in a bed of variable depth; and

(k) wherein fluidization and tramp removal occur without internalcirculation of bed particles within the bed.

These and other objects and features of the present invention will beapparent from the detailed description taken with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in diagrammatic and fragmentary cross section afluidized bed system in accordance with the prior art which utilizes agrid plate;

FIG. 2 is a diagrammatic fragmentary cross section of another prior artfluidized bed system, which utilizes a plurality of air distributionheaders and nozzles accommodating removal of tramp material from a lowerconical section after it passes downwardly between the nozzles and theheaders;

FIG. 3 is a fragmentary cross section of a first presently preferredembodiment of the present invention;

FIG. 4 is a fragmentary cross section partly in perspective whichillustrates a grid plate similar to the embodiment of FIG. 3 with thebed material removal therefrom;

FIG. 5 is a cross section of the grid plate taken along lines 5--5 ofFIG. 4;

FIG. 6 is a bottom plan view of the grid plate of FIG. 4;

FIG. 7 is a cross sectional view taken along lines 7--7 of FIG. 6;

FIG. 8 is another presently preferred embodiment of the presentinvention illustrating a grid plate having a variable non-uniform arrayof fluidizing air apertures contained therein;

FIG. 9 is an enlarged fragmentary cross sectional view of a furtherpresently preferred embodiment of the present invention;

FIG. 10 is a plan view taken along lines 10--10 of FIG. 9;

FIG. 11 is a fragmentary perspective representation of still anotherpresently preferred embodiment in accordance with the present invention;and

FIG. 12 is a fragmentary side elevation of a presently preferredembodiment for separating bed and tramp materials which are removed fromthe vessel and returning the segregated bed material to the vessel.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Specific reference is now made to the drawings in detail wherein likenumerals are used to designate like parts throughout. FIGS. 1 and 2, aspreviously indicated, refer to prior art proposals by which the bedmaterial is retained in the bed vessel and fluidizing air delivered tothe bed, with FIG. 2 further showing structure by which tramp and bedmaterial are removed from the vessel.

FIG. 3 illustrates in fragmentary vertical cross section (somewhat inschematic form) a presently preferred fluidized bed apparatus, generallydesignated 20. Apparatus 20 comprises a generally cylindrical singlevessel 22 formed of suitable steel or refractory lined steel havingcharacteristics adequate to resist the temperatures and abrasiveenvironment existing in the interior thereof during use. The verticallyerect cylindrical vessel 22 comprises a lower end 24 which is closed bya horizontal disc shaped bottom plate 26 and an upper end 27 comprisinga top plate 29.

The interior of the vessel immediately above the bottom 26 consitutes aplenum or wind box 28 into which fluidizing air is introduced from aconventional source (not shown) in the direction of arrow 30 through airinfluent conduit 32 which comprises an opening 34 into the plenum orwindbox 28.

The top of the windbox 28 is defined by disc shaped grid or diffuserplate 36 of uniform thickness throughout which is preferably fastened inan airtight manner at its circumference to the vessel 22. A stationarydisc shaped grid plate 36 is disposed at an acute angle θ in respect tothe horizontal. Plate 36 has no moving parts. This angle is determinedby the particular type of tramp material to be removed from the bed aswell as the type of bed material used. However, the present invention isdirected toward uniform fluidization of a bed having a variable depthdue to the sloped grid plate. To achieve the mentioned uniformfluidization without internal bed circulation, the angle of slope mustbe strictly controlled and must be substantially less than the angle ofrepose of the bed material being used. In this connection it has beendiscovered that a gentle slope (θ) within the range of 5° and 15° iseffective in the removal of bed and tramp material in accordance withand based upon the principles of the present invention, as hereinannunciated.

The grid plate 36 compriscs no bubble caps or tuyeres or nozzles.Therefore, there are no projections for incombustible material toaccumulate or collect. Grid plate 36 comprises a plurality of apertures38 through which fluidizing air is caused to pass into the bed from thewindbox 28. The apertures 38 are sized, located and preferablynon-vertically disposed so as to provide uniform essentially verticalfluidization to a single shallow fluid bed 40, formed of suitable inertgranular material, as hereinafter more fully explained. The bedmaintains a horizontal top surface, so the bed depth range is simplythat resulting from the angle of the distributor plate and the diameterof the vessel. A bed depth at the upper edge of on the order of 18inches is appropriate for most application. Thus, for example, a 6 footdiameter bed with a 10° sloped plate would have an 18 inch deep bed onthe shallow side and a 31 inch deep bed on the deep side.

Separate particles of fuel 12 are introduced into the vessel 22continuously or continually in any one of several ways known to beconventional in the art. Apparatus is provided for continuallydelivering fuel, which may comprise pieces of solid waste 42 to theincineration or pyrolysis fluid bed vessel 22. See FIG. 3. Thereafter,the pieces of solid waste 42 are caused to become somewhat homogeneouslydistributed within a fluidized bed 40 disposed near the bottom of anincineration vessel 26. While any conveyance may be used to so depositthe solid waste pieces 42 within the fluidized bed 40, including thedirect injection of the pieces into the bed, a box conveyor 14 isillustrated in FIG. 3. The leading or top end of the conveyor extendsinto the vessel 22 at elevated opening 11. Conveyor 14 comprises aconveyor belt 16 conventionally driven and displaced around a roller 17whereby the solid waste pieces 42 fall into the vessel and aredistributed by an impact cone 19 which is mounted on a support 21 and isin turn supported by a cross member 23. Mechanisms may be used inconjunction with the box conveyor 14 to meter the rate at which solidwaste pieces are fed into the vessel. As a consequence, the pieces ofsolid waste 42, which, by way of example, may comprise wood waste andlike stock refuge, are caused to be evenly distributed and embeddedwithin the fluidized bed 40.

Depending upon the particular material and circumstances, pieces ofsolid waste 42 may be pre-dried before being fed into the incinerator,or water may be added thereto prior to or simultaneously withdisplacement into the incinerator. In any event, said pices are subjectto high temperature combustion or pyrolysis, with or withoutcarbonaceous residue, depending upon operating temperature, oxygenavailable and mode of operation.

In the course of fuel introduction, non-combustible tramp material 42,e.g. rocks, steel objects, etc., is also typically and inherentlyintroduced with the fuel particles 12 and caused thereafter to beembedded within the fluid bed 40. Due to the weight of the particles 42of tramp material, they are caused by the action of the fluidizing airand the force of gravity to move progressively in a downward directionuntil contact is made with the upper surface 44 of the gently slopedgrid plate 36. Thereafter, the force of gravity in conjunction with thefluidizing air alone causes the tramp particles 42 to walk slowlydownwardly along the top surface 44 of the plate 36 and to beprogressively discharged along with bed material through bed and trampremoval discharge conduit 46 in the direction of arrow 48.

Thus, the removal of tramp is solely by the force of gravity andfluidizing air without internal circulation of the bed while maintaininguniform vertical fluidization of the bed across the entire cross sectionof the bed. At no time is the tramp material passed to a location aboveor below the bed, while in the vessel.

The discharge site 52 is juxtaposed fluidization holes in the grid plate36 and no mass of bed material downstream of the region of fluidizationis required. Although the discharge of fluidized air through the gridplate into the bed is preferably non-vertical, the horizontal componentof said air discharge is immediately dissipated and the bed turbulenceor direction of fluidization is, therefore, essentially vertical.

The grid plate 36 is preferably fastened in an airtight manner into theillustrated position so that the lowest point 52 of the top surface 44of the plate 36 is flush with the low point of the interior of thedischarge conduit 46. Typically, as explained hereinafter in greaterdetail, the discharged bed material is reclaimed after being segregatedfrom the discharge tramp material, at which time the discharged trampmaterial is discarded.

During fluidization, even though the size of the granular particlesforming the bed 40 and the size of some of the tramp material particles42 may have a transverse dimension less than the diameter of the plateapertures 38, none of the bed or tramp material particles will passthrough the grid plate 36 due to the force of fluidizing air passingupwardly therethrough into the bed 40.

During periods of non-use and/or non-fluidization, the bed material iskept from falling into the plenum 28 by use of bed containment structurewhich are illustrated as being in the form of half sections of steelpipe 50. The half sections of pipe 50 are preferably welded at theiredges to the underside of the plate 36 directly under one or more gasdistributor apertures 38. When no fluidizing air is being passed throughthe grid plate 36, a very limited amount of bed material falls into eachhalf section of pipe 50 beneath the plate 36. A small pile of bedmaterial thus accumulates beneath each hole in the associated halfsection of pipe 50 and serves after a brief period of time to clog eachassociated aperture 38 to prevent further flow of bed material. Theamount of material accumulated in each half section pipe 50 depends uponthe size of the apertures and the angle of repose of the bed material.No bed material falls into the plenum or windbox 28.

When air is again admitted into the plenum and fluidization undertaken,the air passes through the open ends 54 (FIG. 7) of each pipe section 50in opposite directions as denoted by arrows 55. This air pneumaticallysweeps the accumulated bed particles through the associated aperture orapertures 38 back into the bed 40.

Because the air distributor apertures 38 in the illustrated embodimentsare disposed at right angles to the grid plate 36, air enters the bed inone or more non-vertical directions. Air entering the bed in suchnon-vertical directions is controlled to enhance the slow migration ofthe tramp material downwardly along the top surface 44 of the grid plate36 to the lower site 52 where discharge from the vessel 22 occurs, aspreviously mentioned. The degree to which the air enters the bed in oneor more non-vertical directions is directly related to the slope angle θof the plate. Secondary air is not required for tramp removal.

It should be noted, with reference to FIG. 4, that the disposition ofplate 36 is illustrated as being skewed (i.e. disposed at acute anglesin respect to a horizontal plane and two vertical planes eachperpendicular with the horizontal plane and perpendicular to eachother). Use of a skewed distributor plate provides for a longer dwelltime for fuel particles incinerated or pyrolyzed within the bed 40. Thedwell time of fuel particles 12 in the bed 40 may be controlled bycontrolling the rate and points in time when bed material and trampmaterial are caused to be discharged from the vessel 22 throughdischarge conduit 46.

As can be seen by observance of FIGS. 5-7, the half section pipes 50 maybe of various lengths selected to be disposed beneath the grid plate 16so as to cover at least one and preferably two or three of the gridapertures 38. Preferably the bed containment half section pipes 50 arebutt welded to the lower surface of the grid plate 36, as illustrated.

It should be readily apparent, with reference to presently preferredembodiment 100 (illustrated in FIG. 8), that in some applications auniform spacing of air distribution apertures 38 in the grid plate 36may not be sufficient to promote uniform fluidization of the bed 40.Accordingly, variations may be made in the size and arrangement of theapertures 38 so as to promote uniform fluidization of the entire bed.

Ordinarily, depending upon the bed material being used and the fuel andtramp material being fed into the vessel 22, it is preferable to have ahigher density of apertures in the lower portion of the grid plate 36 asopposed to the more elevated portion of the grid plate. An array ofapertures consistent with the principles of the present invention, whichprovides a more dense hole spacing toward the bottom of the inclinewhich gives the same vertical air velocity through the deeper portion ofthe bed as occurs in the shallower portion of the bed, is illustrated inFIG. 8. In other words, the variation in fluidizing aperture densityprovides uniform vertical air flow across the entirety of the bed, whichhas a variable depth. Other variations in the aperture array can beutilized, it being a requirement of the present invention that apressure drop through the grid plate 36 of at least 30% of pressure dropthrough the bed 40 be achieved by air distributed through each aperture38 of the grid plate 44. Any distribution of holes 38, properly sizedand arranged of a low density at the high side of the plate to a highdensity at the low side of the plate may be utilized which achieves thementioned pressure drop and uniform bed fluidization.

When using a flat distributor plate, the distributor plate pressure, asmentioned, drop for uniform fluidization is about 1/3 that of the bedpressure drop. For a sloped plate the 1/3 factor applies to the deepestpart of the bed. Therefore, the plate pressure drop on the shallow sidemust be greater to keep the air from preferentially going through thatpart of the bed. The desired pressure drop, which varies with bed depth,can be obtained by either a small number of large holes, or a largenumber of small holes in the region where the bed is deepest.

Thus, in the six foot bed example, the flat distributor must have a 0.55psi pressure drop on the deep side and a 1.02 psi drop on the shallowside. If 3/16 inch diameter holes are used, the hole "density" would be244 holes/ft² on the deep side and progress to 180 holes/ft² on theshallow side. Similarly, if 1/4 inch diameter holes are used throughout,the hole density ranges from 137 holes/ft² to 101 holes/ft².

A further presently preferred embodiment in accordance with the presentinvention is illustrated in FIGS. 9 and 10 and is generally designated102. The illustrations of FIGS. 9 and 10 are somewhat exaggerated inlength and slope for purposes of visual clarity. Fluidized bed system102 is identical in most major respects to fluidized bed system 20already described and identical parts have been labeled identically toavoid presentation of duplicative descriptive information. Fluidized bedsystem 102 comprises the air influent duct 32 which delivers air underpressure to the plenum or windbox 28, the bed and tramp materialdischarge duct 32 as well as an influent duct 104 by which new and/orreclaimed bed material is introduced. Fuel is introduced on a controlledor metered basis.

The system 102 also comprises the previously described sloped grid plate36 having an essentially uniform array of fluidizing air apertures 38perpendicularly disposed therein. The grid plate 36 (not illustrated inFIG. 9), is disposed at a gentle acute angle in respect to thehorizontal. The location and slope of the plate 36 is such that bed andtramp material entering the vessel 22 at influent conduit 104 is causedto flow solely by forces of gravity and fluidizing air from bed materialinfluent 104 downwardly along the serpentine flow path 106 (FIGS. 9 and10) to discharge duct 46. The mentioned serpentine bed materialdisplacement along flow path 106 is enhanced by the presence of two bedpath deflecting upright baffle plates 108 and 110, which arerespectively welded to the top surface 44 of the plate 36 at an edgethereof so as to project a substantial distance in a generally verticaldirection. The height of the baffle plates 108 and 110 is selected so asto be a function of bed and tramp material over the top of eitherbaffle. Baffle 108 is contiguous at edge 112 with and preferably weldedto the vessel, as is edge 114 of baffle 110.

Baffle ends 116 and 118 are spaced from the wall of the vessel 22 andaccommodate the described serpentine flow of bed material containingtramp. In this way, a uniform array of apertures is satisfactory and thetop surface of the bed may be sloped at an angle to the horizontalrequiring minimal custom design of the grid plate to achieve properuniform bed fluidization.

In addition, utilization of the baffles 108 and 110 materially increasethe dwell time for particles of fuel 12 being incinerated or pyrolyzedin the bed so that such fuel is adequately oxidized prior to reachingthe discharge duct 46.

Reference is now made to FIG. 11, which illustrates a further presentlypreferred fluidized bed system embodiment in accordance with the presentinvention, which is generally designated 140. Since some of the parts ofsystem 140 are substantially identical to components of previouslydescribed systems 20 and 102, those components have been given numeralsidentical to the numerals used in conjunction with the prior detaileddescription of the systems 20 and 102 and no further description ofthose components is deemed needed.

System 140 comprises a serpentine shaped grid or air diffusion plate 142located in the lower part of the vessel 22 and having an outside edge144 contiguous with and fastened to the interior surface of the steelvessel 22. Serpentine grid plate 142 also comprises heretofore describedfluidizing air apertures 38. Grid plate 144 also comprises severalinterior edges 146 which are contiguous with and fastened to one side orthe other of one or the other of a pair of vertically directed upper andlower baffle plates 108 and 110. It should be apparent that there arefour linear edges 146, each sloped baffle plate 108 being contiguous atthe bottom of the plate with two such edges 146. The two edges 146 ofbaffle plate 108 runs from an elevation at site 150 adjacent the bedmaterial influent conduit 104 through a 180° turn to site 152.Similarly, baffle plate 110 contiguously receives two plate edges 146which run downwardly through a 180° turn in a continuous fashion fromsite 154 to site 156. It should be apparent from observation of FIG. 11that site 150 has an elevation higher than site 152, which has anelevation higher than site 154 which has an elevation above site 156.Site 156 is directly adjacent the intake opening to bed and trampmaterial effluent conduit 46. By controlling the slope of serpentineplate 142 and the rate and frequency of which bed material is introducedat conduit 104 and tramp material and bed material are discharged atconduit 46, the dwell time of the bed material, tramp material and fuelwithin the vessel 22 is controlled to produce continuous and properfluidization of the bed as well as satisfactory fuel incineration orpyrolysis.

As mentioned earlier, the granular bed material and tramp material whichwalks or migrates into discharge duct 46 is segregated. FIG. 12illustrates presently preferred embodiment, generally designated 160,which segregates the tramp from the discharged bed material, discardsthe tramp and recycles or returns the bed material to the vessel 22.Discharged tramp and bed material, in respect to FIG. 12, pass fromdischarge duct 46 around elbow 162, along duct 164 and vertically outthe exposed discharge end 166 of duct 164. Thus, the tramp and bedmaterial are discharged vertically onto a vibrating screen conveyor 168,which is driven by motor M1 so as to oscillate. The screen conveyor 168separates reusable bed material from tramp material with the trampmaterial proceeding up the conveyor 168, off the elevated end 170 anddiscarded into a portable refuge container 172. The reusable bedmaterial passes through the mesh of the conveyor 168 onto a lowerconveyor 174 and is discharged from the elevated end 176 thereof into abed material storage bin 178 into a bed material return conduit 180along which the return bed materially is displaced and ultimately outeffluent end 182 thereof onto the fluidized bed 40 within the vessel 22under force of blower 184 driven by motor M2. Thus, tramp material isremoved and the bed material is continuously or intermittentlyrecirculated for reuse. The bin 178 also provides a convenient point forthe addition of new "makeup" bed material which is required from time totime during normal operation of the fluid bed system, due to particleelutriation and attrition caused by particle fracture and abrasive wear.In this way, the bed inventory is maintained at the optimum level forproper uniform fluidization.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore considered in all respects as illustrative andnot restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:
 1. A method of uniformly fluidizing a variable depth fluidbed while progressively removing tramp material from the bed without useof moving parts comprising the steps of:providing a single fluid bed ina vessel so that the depth of the bed varies along the transverse crosssection of the bed; supporting the entire fluid bed upon an inclinedstationary grid plate having an array of fluidizing apertures but nomoving parts, the stationary grid plate having an angle with respect tothe horizontal less than the angle of repose of the bed material;introducing a plurality of separate fuel particles and non-combustibletramp material into the vessel and the fluid bed; providing fluidizingair under pressure to a plenum beneath the stationary grid plate anddirecting the air through the array of apertures in the grid plate touniformly vertically fluidize the entire bed and to gently walk thetramp down the incline of the stationary grid plate to a vesseldischarge site solely by the forces of gravity and fluidizing air;preventing flow loss of bed particles through the apertures into theplenum both while the bed is fluidized and not fluidized.
 2. A methodaccording to claim 1 wherein the walking of tramp is circuitous upon thestationary grid plate.
 3. A method according to claim 1 wherein thedirecting air through the grid plate comprises displacing the airthrough the aperture at one or more non-vertical angles.
 4. A methodaccording to claim 1 wherein the discharged bed and tramp materials aresegregated one from the other and the segregated bed material returnedto the fluid bed within the vessel.